[Lldb-commits] [lldb] [LLDB] Added support for cross compiling with host python (PR #123735)

[via lldb-commits]

https://github.com/patryk4815 updated https://github.com/llvm/llvm-project/pull/123735

>From 1883c703f335d44f5a4cfff8148c8d557ab6af1e Mon Sep 17 00:00:00 2001
From: Patryk Sondej <patryk.sondej at grupawp.pl>
Date: Tue, 21 Jan 2025 12:44:44 +0100
Subject: [PATCH 1/2] Added support for `_PYTHON_HOST_PLATFORM` and
 `_PYTHON_SYSCONFIGDATA_NAME` environment variables when cross-compiling LLDB
 with Python, https://peps.python.org/pep-0720/#upstream-support

---
 lldb/CMakeLists.txt | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/lldb/CMakeLists.txt b/lldb/CMakeLists.txt
index 85ba4fde17418a..d11c68dd5b96af 100644
--- a/lldb/CMakeLists.txt
+++ b/lldb/CMakeLists.txt
@@ -59,8 +59,23 @@ if (LLDB_ENABLE_PYTHON)
   set(cachestring_LLDB_PYTHON_EXT_SUFFIX
     "Filename extension for native code python modules")
 
+  set(LLDB_USE_HOST_PYTHON FALSE)
+  if(NOT CMAKE_CROSSCOMPILING)
+    set(LLDB_USE_HOST_PYTHON TRUE)
+  else()
+    # Used when cross-compiling LLDB with Python:
+    # - `_PYTHON_HOST_PLATFORM`: Specifies the host platform, e.g., 'linux-x86_64'.
+    # - `_PYTHON_SYSCONFIGDATA_NAME`: The name of the Python configuration module containing
+    #   platform, build, and configuration details (e.g., `_sysconfigdata__linux_x86_64-linux-gnu`).
+    # See: https://peps.python.org/pep-0720/#upstream-support
+    # If both environment variables are defined, we assume host Python can be used.
+    if(DEFINED ENV{_PYTHON_HOST_PLATFORM} AND DEFINED ENV{_PYTHON_SYSCONFIGDATA_NAME})
+      set(LLDB_USE_HOST_PYTHON TRUE)
+    endif()
+  endif()
+
   foreach(var LLDB_PYTHON_RELATIVE_PATH LLDB_PYTHON_EXE_RELATIVE_PATH LLDB_PYTHON_EXT_SUFFIX)
-    if(NOT DEFINED ${var} AND NOT CMAKE_CROSSCOMPILING)
+    if(NOT DEFINED ${var} AND LLDB_USE_HOST_PYTHON)
       execute_process(
         COMMAND ${Python3_EXECUTABLE}
           ${CMAKE_CURRENT_SOURCE_DIR}/bindings/python/get-python-config.py

>From 2bcb3ca530cc77a975542a36027d986ff05efea5 Mon Sep 17 00:00:00 2001
From: Patryk Sondej <patryk.sondej at grupawp.pl>
Date: Wed, 22 Jan 2025 05:06:31 +0100
Subject: [PATCH 2/2] get-python-config.py: Replace all sys.* references with
 sysconfig.get_config_var calls

---
 lldb/bindings/python/get-python-config.py | 28 +++++++++++++++++------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/lldb/bindings/python/get-python-config.py b/lldb/bindings/python/get-python-config.py
index ae84cbb1215a9e..82fc11dd3997ed 100755
--- a/lldb/bindings/python/get-python-config.py
+++ b/lldb/bindings/python/get-python-config.py
@@ -1,5 +1,14 @@
 #!/usr/bin/env python3
 
+# In this script, we should only use the following to retrieve configuration values:
+# - `sysconfig.get_config_var`
+# - `sysconfig.get_platform`
+# - `sysconfig.get_path`
+# This is because certain variables may return invalid data during cross-compilation, for example:
+# - sys.prefix -> Use sysconfig.get_config_var("prefix") instead.
+# - sys.executable -> Use sysconfig.get_config_var("EXENAME") instead.
+# - os.name -> Use sysconfig.get_platform() for platform detection.
+
 import os
 import sys
 import argparse
@@ -32,20 +41,25 @@ def main():
         # If not, you'll have to use lldb -P or lldb -print-script-interpreter-info
         # to figure out where it is.
         try:
-            print(relpath_nodots(sysconfig.get_path("platlib"), sys.prefix))
+            print(relpath_nodots(sysconfig.get_path("platlib"), sysconfig.get_config_var("prefix")))
         except ValueError:
             # Try to fall back to something reasonable if sysconfig's platlib
             # is outside of sys.prefix
             if os.name == "posix":
-                print("lib/python%d.%d/site-packages" % sys.version_info[:2])
+                print("lib/python%s/site-packages" % sysconfig.get_config_var("VERSION"))
             elif os.name == "nt":
                 print("Lib\\site-packages")
             else:
                 raise
     elif args.variable_name == "LLDB_PYTHON_EXE_RELATIVE_PATH":
         tried = list()
-        exe = sys.executable
-        prefix = os.path.realpath(sys.prefix)
+        exe = sysconfig.get_config_var("EXENAME")
+        if not exe:
+            # Fallback: 'EXENAME' is not available on Windows
+            exe_name = "python" + sysconfig.get_config_var("VERSION") + sysconfig.get_config_var("EXE")
+            exe = os.path.join(sysconfig.get_config_var("BINDIR"), exe_name)
+
+        prefix = os.path.realpath(sysconfig.get_config_var("prefix"))
         while True:
             try:
                 print(relpath_nodots(exe, prefix))
@@ -59,13 +73,13 @@ def main():
                     continue
                 else:
                     print(
-                        "Could not find a relative path to sys.executable under sys.prefix",
+                        "Could not find a relative path to sysconfig.get_config_var(\"EXENAME\") under sysconfig.get_config_var(\"prefix\")",
                         file=sys.stderr,
                     )
                     for e in tried:
                         print("tried:", e, file=sys.stderr)
-                    print("realpath(sys.prefix):", prefix, file=sys.stderr)
-                    print("sys.prefix:", sys.prefix, file=sys.stderr)
+                    print("realpath(sysconfig.get_config_var(\"prefix\")):", prefix, file=sys.stderr)
+                    print("sysconfig.get_config_var(\"prefix\"):", sysconfig.get_config_var("prefix"), file=sys.stderr)
                     sys.exit(1)
     elif args.variable_name == "LLDB_PYTHON_EXT_SUFFIX":
         print(sysconfig.get_config_var("EXT_SUFFIX"))